Human Cytomegalovirus (HCMV) is the major viral cause of birth defects, infecting 1-2 percent of all newborns annually. Approximately 5-10 percent of these congenitally infected infants will manifest signs of serious neurological damage at birth which can include deafness, blindness, mental retardation and microcephaly. Another 10-15 percent will develop sensori-neural hearing loss and/or learning disabilities within the first 10 years of life. Our long-term goal is to understand the mechanism behind the development of morbidity and mortality in infants congenitally infected with HCMV. To this end, we have studied the interaction of HCMV with the cell cycle and DNA repair machinery of the permissively infected cell over the last several years. What we have discerned is that HCMV sequesters many of the key players of maintenance and repair into its viral replication centers. However, it appears to partition the components of several complexes so that all the proteins are present within the replication centers, but not all are available to the cellular genome. We have also determined that HCMV can induce very specific genotoxic damage at positions 1q21 and 1q42 when cells are infected during S-phase. Coupled with reports of others regarding the nonspecific damage induced at late times post infection, it is becoming more clear that HCMV is indeed genotoxic to the host cell genome. We hypothesize that long-term detrimental consequences to the cellular genome may occur if 1) this initial specific damage is propagated or 2)damage incurred at late times post infection is not repaired due to sequestration of the repair machinery. To test our hypothesis, we propose three specific aims. First, we will thoroughly define the parameters of chromosome 1q breakage in HCMV-infected cells with regard to rapidity of induction and cell cycle phase at time of infection. We will also determine what virion components are required for break induction. We think it is imperative that our results be moved into more clinically relevant cell types, especially cells of neural lineage, as these are the cells most severely affected by the virus during congenital infection. Second, we also will determine the consequences of chromosome 1 damage in these clinically relevant cells, and whether in a semi-permissive environment we can observe propagation of the chromosome 1 damage instead of healing of the break or movement of the cell toward apoptosis. Lastly, we will characterize the ability of HCMV-infected cells to repair exogenously introduced damage at late times post infection, after viral replication centers are assembled. It is our belief that results we obtain in culture will aid in our understanding of the central nervous system problems observed in congenitally infected infants.